This invention relates to a process of separating the special steel content from lump shredder scrap from which the ferromagnetic content has been separated before.
From ecological and economic aspects, the recycling of useful materials recovered from waste materials is increasing in significance. Glass and paper are being separately collected on a large scale so that the used materials can be re-utilized in substantial quantities. In some areas, even plastics are selectively collected and are processed for their further use. Large-scale tests are presently being conducted regarding the recycling of beverage cans by means of automatic collecting machines.
In all of the examples mentioned, the recycling is facilitated because it is relatively easy to selectively collect the waste materials. But this is not the case with most waste material and the useful materials contained therein cannot be used unless suitable separating processes can be made available. A process or apparatus can be deemed suitable if it permits individual components or groups of materials to be separated from mixed waste materials as completely as possible and with the highest possible purity and if the expenditure involved is reasonably related to the value added.
In the Federal Republic of Germany, scrap from shredder plants becomes available at a rate of about 2 million tons per year. That scrap has the following composition:
70% ferromagnetic metals PA1 10% nonferromagnetic metals PA1 20% nonmetals
When the ferromagnetic metals are magnetically separated and the remaining scrap has been subjected to air separation, the resulting blend consisting of about 50% metallic materials and 50% nonmetallic materials is divided by sieving into a normal size fraction and an undersize fraction. In dependence on the intended further processing, the limiting size is selected between sieve analysis particle sizes of 12 and 25 mm. Whereas the normal size fraction is suitable for a further sorting by singling and analysis of the individual pieces or for a manual sorting, the undersize fraction could not be subjected to such processes with economically satisfactory results.
In addition to rubber, plastic, glass, stones, etc., the undersize fraction still contains about 30% metal, with average contents of 9% copper and brass, 12% aluminum, 3% zinc, 2% lead and 4% special steel or stainless steel. In an unsorted state that metal content has a value of DM 80 per 1000 kg and of about DM 2000 per 1000 kg in a completely sorted state.
Wet separating processes (performed by sink-float apparatus or jigs) are usually employed to remove from the undersize fraction the organic constituents (rubber, plastic, textiles) in a first pass and to effect a division into light and heavy fractions in a second pass. The light fraction contains about 30% aluminum, balance stones, broken glass and plastics and pieces of insulated copper wire and must be dumped because said components cannot yet be separated by an economic process. On the other hand, the heavy fraction is processed further almost exclusively by a fractional melting process in the previous practice. That process results in the production of ingots of lead and zinc, which contain about 90% lead and zinc, respectively, and in a balance consisting of a mixed scrap consisting of copper, brass and special steel. The price which is paid for that residual scrap, which contains about 60% copper and brass, is less by 450 to 550 DM per 1000 kg than the price paid for a similar scrap which is free from special steel. Pure special steel scrap costs 1000 DM, per 1000 kg. This means that the worth per 1000 kg of the underside fraction can be increased by DM 85 if the special steel can be separated from the residual scrap blend. Further advantages will be afforded if the special steel fraction is separated before the fractional melting process or even before the wet separating steps.
For this reason it is an object to provice in connection with the process mentioned first hereinbefore a method by which the special steel content can economically be separated from the undersize fraction of shredder scrap.